Self calibration of downlink transmit power

ABSTRACT

Transmit power (e.g., maximum transmit power) may be defined based on the maximum received signal strength allowed by a receiver and a total received signal strength from transmitting nodes at the receiver. Transmit power may be defined for an access node (e.g., a femto node) such that a corresponding outage created in a cell (e.g., a macro cell) is limited while still providing an acceptable level of coverage for access terminals associated with the access node. An access node may autonomously adjust its transmit power based on channel measurement and a defined coverage hole to mitigate interference and perform a self-calibration process.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application for patent is a continuation of U.S. patentapplication Ser. No. 12/463,714, entitled “SELF CALIBRATION OF DOWNLINKTRANSMIT POWER,” filed May 11, 2009, pending, which claims the benefitof U.S. Provisional Application No. 61/052,969, entitled “SYSTEM,APPARATUS, AND METHOD TO ENABLE FEMTOCELL SELF CALIBRATION OF DOWN LINKTRANSMIT POWER,” filed May 13, 2008, each assigned to the assigneehereof, and each expressly incorporated herein by reference in itsentirety.

BACKGROUND

1. Field

This application relates generally to wireless communication and morespecifically, but not exclusively, to improving communicationperformance.

2. Background

Wireless communication systems are widely deployed to provide varioustypes of communication (e.g., voice, data, multimedia services, etc.) tomultiple users. As the demand for high-rate and multimedia data servicesrapidly grows, there lies a challenge to implement efficient and robustcommunication systems with enhanced performance.

To supplement the base stations of a conventional mobile phone network(e.g., a macro cellular network), small-coverage base stations may bedeployed, for example, in a user's home. Such small-coverage basestations are generally known as access point base stations, home nodeBs,or femto cells and may be used to provide more robust indoor wirelesscoverage to mobile units. Typically, such small-coverage base stationsare connected to the Internet and the mobile operator's network via aDSL router or a cable modem.

In a typical macro cellular deployment the RF coverage is planned andmanaged by cellular network operators to optimize coverage. Femto basestations, on the other hand, may be installed by the subscriberpersonally and deployed in an ad-hoc manner. Consequently, femto cellsmay cause interference both on the uplink (“UL”) and downlink (“DL”) ofthe macro cells. For example, a femto base station installed near awindow of a residence may cause significant downlink interference to anyaccess terminals outside the house that are not served by the femtocell. Also, on the uplink, home access terminals that are served by afemto cell may cause interference at a macro cell base station (e.g.,macro nodeB).

Interference between the macro and femto deployments may be mitigated byoperating the femto network on a separate RF carrier frequency than themacro cellular network.

Femto cells also may interfere with one another as a result of unplanneddeployment. For example, in a multi-resident apartment, a femto basestation installed near a wall separating two residences may causesignificant interference to a neighboring residence. Here, the strongestfemto base station seen by a home access terminal (e.g., strongest interms of RF signal strength received at the access terminal) may notnecessarily be the serving base station for the access terminal due to arestricted association policy enforced by that femto base station.

RF interference issues may thus arise in a communication system whereradio frequency (“RF”) coverage of femto base stations is not optimizedby the mobile operator and where deployment of such base stations isad-hoc. Thus, there is a need for improved interference management forwireless networks.

SUMMARY

A summary of sample aspects of the disclosure follows. It should beunderstood that any reference to the term aspects herein may refer toone or more aspects of the disclosure.

The disclosure relates in some aspect to determining transmit power(e.g., maximum power) based on the received signal strength of abest-reception macro access node and the received signal strength fromall other nodes. In this way, the access node (e.g., femto node) canadaptively adjust the transmit power level depending on the macro accessnode signal levels and other femto node signals.

The disclosure relates in some aspects to defining transmit power for anaccess node (e.g., a femto node) such that a corresponding outage (e.g.,a coverage hole) created in a cell (e.g., a macro cell) is limited whilestill providing an acceptable level of coverage for access terminalsassociated with the access node. In some aspects, these techniques maybe employed for coverage holes in adjacent channels (e.g., implementedon adjacent RF carriers) and in co-located channels (e.g., implementedon the same RF carrier).

The disclosure relates in some aspects to autonomously adjustingdownlink transmit power at an access node (e.g., a femto node) tomitigate interference. In some aspects, the transmit power is adjustedbased on channel measurement and a defined coverage hole. Here, a mobileoperator may specify coverage hole and/or channel characteristics usedto adjust the transmit power.

In some implementations an access node measures the received signalstrength of signals from a macro access node and determines transmissionpower limits relating to the coverage hole in the macro cell. Based onthe transmission power limits, the access node may select a particulartransmit power value. For example, transmit power at the access node maybe adjusted based on received signal strength of the best-receptionmacro access node and the received signal strength from all other nodes.

The disclosure relates in some aspects to defining transmit power basedon received signal strength of the best-reception macro access node andthe received signal strength from all other nodes. For example, anaccess node may commence operation with a default transmit power (e.g.,pilot fraction value) when it is installed and later dynamically adjustthe transmit power based on received signal strength of thebest-reception macro access node and the received signal strength fromall other nodes.

The disclosure relates in some aspects to adaptively adjusting thedownlink transmit power of neighboring access nodes. In some aspects,sharing of information between access nodes may be utilized to enhancenetwork performance. For example, if an access terminal is experiencinghigh interference levels from a neighboring access node, informationrelating to this interference may be relayed to the neighbor access nodevia the home access node of the access terminal. As a specific example,the access terminal may send a neighbor report to its home access node,whereby the report indicates the received signal strength the accessterminal sees from neighboring access nodes. The access node may thendetermine whether the home access terminal is being unduly interferedwith by one of the access nodes in the neighbor report. If so, theaccess node may send a message to the interfering access node requestingthat the access node reduce its transmit power. Similar functionalitymay be achieved through the use of a centralized power controller.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other sample aspects of the disclosure will be described inthe detailed description and the appended claims that follow, and in theaccompanying drawings, wherein:

FIG. 1 is a simplified diagram of several sample aspects of acommunication system including macro coverage and smaller scalecoverage;

FIG. 2 is a simplified block diagram of several sample aspects of anaccess node;

FIG. 3 is a flowchart of several sample aspects of operations that maybe performed to determine transmit power based on received signalstrength of the best-reception macro access node and the maximumreceived signal strength from all other nodes;

FIG. 4 is a flowchart of several sample aspects of operations that maybe performed to determine transmit power based on signal-to-noise ratio;

FIG. 5 is a simplified diagram illustrating coverage areas for wirelesscommunication;

FIG. 6 is a simplified diagram of several sample aspects of acommunication system including neighboring femto cells;

FIG. 7 is a flowchart of several sample aspects of operations that maybe performed to control transmit power of a neighboring access node;

FIG. 8 is a flowchart of several sample aspects of operations that maybe performed to adjust transmit power in response to a request fromanother node;

FIG. 9 is a simplified diagram of several sample aspects of acommunication system including centralized power control;

FIG. 10 is a flowchart of several sample aspects of operations that maybe performed to control transmit power of an access node usingcentralized power control;

FIGS. 11A and 11B are a flowchart of several sample aspects ofoperations that may be performed to control transmit power of an accessnode using centralized power control;

FIG. 12 is a simplified diagram of a wireless communication systemincluding femto nodes;

FIG. 13 is a simplified block diagram of several sample aspects ofcommunication components; and

FIGS. 14-15 are simplified block diagrams of several sample aspects ofapparatuses configured to provide power control as taught herein.

In accordance with common practice the various features illustrated inthe drawings may not be drawn to scale. Accordingly, the dimensions ofthe various features may be arbitrarily expanded or reduced for clarity.In addition, some of the drawings may be simplified for clarity. Thus,the drawings may not depict all of the components of a given apparatus(e.g., device) or method. Finally, like reference numerals may be usedto denote like features throughout the specification and figures.

DETAILED DESCRIPTION

Various aspects of the disclosure are described below. It should beapparent that the teachings herein may be embodied in a wide variety offorms and that any specific structure, function, or both being disclosedherein is merely representative. Based on the teachings herein oneskilled in the art should appreciate that an aspect disclosed herein maybe implemented independently of any other aspects and that two or moreof these aspects may be combined in various ways. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, such an apparatusmay be implemented or such a method may be practiced using otherstructure, functionality, or structure and functionality in addition toor other than one or more of the aspects set forth herein. Furthermore,an aspect may comprise at least one element of a claim.

FIG. 1 illustrates sample aspects of a network system 100 that includesmacro scale coverage (e.g., a large area cellular network such as a 3Gnetwork, which may be commonly referred to as a macro cell network) andsmaller scale coverage (e.g., a residence-based or building-basednetwork environment). As a node such as access terminal 102A movesthrough the network, the access terminal 102A may be served in certainlocations by access nodes (e.g., access node 104) that provide macrocoverage as represented by the area 106 while the access terminal 102Amay be served at other locations by access nodes (e.g., access node 108)that provide smaller scale coverage as represented by the area 110. Insome aspects, the smaller coverage nodes may be used to provideincremental capacity growth, in-building coverage, and differentservices (e.g., for a more robust user experience).

As will be discussed in more detail below, the access node 108 may berestricted in that it may not provide certain services to certain nodes(e.g., a visitor access terminal 102B). As a result, a coverage hole(e.g., corresponding to the coverage area 110) may be created in themacro coverage area 106.

The size of the coverage hole may depend on whether the access node 104and the access node 108 are operating on the same frequency carrier. Forexample, when the nodes 104 and 108 are on a co-channel (e.g., using thesame frequency carrier), the coverage hole may correspond to thecoverage area 110. Thus, in this case the access terminal 102A may losemacro coverage when it is within the coverage area 110 (e.g., asindicated by the phantom view of the access terminal 102B).

When the nodes 104 and 108 are on adjacent channels (e.g., usingdifferent frequency carriers), a smaller coverage hole 112 may becreated in the macro coverage area 106 as a result of adjacent channelinterference from the access node 108. Thus, when the access terminal102A is operating on an adjacent channel, the access terminal 102A mayreceive macro coverage at a location that is closer to the access node108 (e.g., just outside the coverage area 112).

Depending on system design parameters, the co-channel coverage hole maybe relatively large. For example, when the transmit power of the smallscale node 108 is 0 dBm, the radius for which the interference of thesmall scale node 108 is at least the same as the thermal noise floor maybe on the order of 40 meters, assuming free space propagation loss and aworst case where there is no wall separation between the small scalenode 108 and access terminal 102B.

A tradeoff thus exists between minimizing the outage in the macrocoverage while maintaining adequate coverage within a designated smallerscale environment (e.g., femto node coverage inside a home). Forexample, when a restricted femto node is at the edge of the macrocoverage, as a visiting access terminal approaches the femto node, thevisiting access terminal is likely to lose macro coverage and drop thecall. In such a case, one solution for the macro cellular network wouldbe to move the visitor access terminal to another carrier (e.g., wherethe adjacent channel interference from the femto node is small). Due tolimited spectrum available to each operator, however, the use ofseparate carrier frequencies may not always be practical. Consequently,a visitor access terminal associated with that other operator may sufferfrom the coverage hole created by the restricted femto node on thatcarrier.

As will be described in detail in conjunction with FIGS. 2-11B, atransmit power value for a node may be defined to manage suchinterference and/or address other similar issues. In someimplementations, the defined transmit power may relate to at least oneof: a maximum transmit power, transmit power for a femto node, ortransmit power for transmitting a pilot signal (e.g., as indicated by apilot fraction value).

For convenience, the following describes various scenarios wheretransmit power is defined for a femto node deployed within a macronetwork environment. Here, the term macro node refers in some aspects toa node that provides coverage over a relatively large area. The termfemto node refers in some aspects to a node that provides coverage overa relatively small area (e.g., a residence). A node that providescoverage over an area that is smaller than a macro area and larger thana femto area may be referred to as a pico node (e.g., providing coveragewithin a commercial building). It should be appreciated that theteachings herein may be implemented with various types of nodes andsystems. For example, a pico node or some other type of node may providethe same or similar functionality as a femto node for a different (e.g.,larger) coverage area. Thus, a pico node may be restricted, a pico nodemay be associated with one or more home access terminals, and so on.

In various applications, other terminology may be used to reference amacro node, a femto node, or a pico node. For example, a macro node maybe configured or referred to as an access node, base station, accesspoint, eNodeB, macro cell, macro nodeB (“MNB”), and so on. Also, a femtonode may be configured or referred to as a home nodeB (“HNB”), homeeNodeB, access point base station, femto cell, and so on. Also, a cellassociated with a macro node, a femto node, or a pico node may bereferred to as a macro cell, a femto cell, or a pico cell, respectively.In some implementations, each cell may be further associated with (e.g.,divided into) one or more sectors.

As mentioned above, a femto node may be restricted in some aspects. Forexample, a given femto node may only provide service to a limited set ofaccess terminals. Thus, in deployments with so-called restricted (orclosed) association, a given access terminal may be served by the macrocell mobile network and a limited set of femto nodes (e.g., femto nodesthat reside within a corresponding user residence).

The restricted provisioned set of access terminals associated arestricted femto node (which may also be referred to as a ClosedSubscriber Group Home nodeB) may be temporarily or permanently extendedas necessary. In some aspects, a Closed Subscriber Group (“CSG”) may bedefined as the set of access nodes (e.g., femto nodes) that share acommon access control list of access terminals. In some implementations,all femto nodes (or all restricted femto nodes) in a region may operateon a designated channel, which may be referred to as the femto channel.

Various relationships may be defined between a restricted femto node anda given access terminal. For example, from the perspective of an accessterminal, an open femto node may refer to a femto node with norestricted association. A restricted femto node may refer to a femtonode that is restricted in some manner (e.g., restricted for associationand/or registration). A home femto node may refer to a femto node onwhich the access terminal is authorized to access and operate. A guestfemto node may refer to a femto node on which an access terminal istemporarily authorized to access or operate. An alien femto node mayrefer to a femto node on which the access terminal is not authorized toaccess or operate, except for perhaps emergency situations (e.g., 911calls).

From the perspective of a restricted femto node, a home access terminal(or home user equipment, “HUE”) may refer to an access terminal that isauthorized to access the restricted femto node. A guest access terminalmay refer to an access terminal with temporary access to the restrictedfemto node. An alien access terminal may refer to an access terminalthat does not have permission to access the restricted femto node,except for perhaps emergency situations such as 911 calls. Thus, in someaspects an alien access terminal may be defined as one that does nothave the credentials or permission to register with the restricted femtonode. An access terminal that is currently restricted (e.g., deniedaccess) by a restricted femto cell may be referred to herein as avisitor access terminal. A visitor access terminal may thus correspondto an alien access terminal and, when service is not allowed, a guestaccess terminal.

FIG. 2 illustrates various components of an access node 200 (hereafterreferred to as femto node 200) that may be used in one or moreimplementations as taught herein. For example, different configurationsof the components depicted in FIG. 2 may be employed for the differentexamples of FIGS. 3-11B. It should thus be appreciated that in someimplementations a node may not incorporate all of the componentsdepicted in FIG. 2 while in other implementations (e.g., where a nodeuses multiple algorithms to determine a transmit power) a node mayemploy most or all of the components depicted in FIG. 2.

Briefly, the femto node 200 includes a transceiver 202 for communicatingwith other nodes (e.g., access terminals). The transceiver 202 includesa transmitter 204 for sending signals and a receiver 206 for receivingsignals. The femto node 200 also includes a transmit power controller208 for determining transmit power (e.g., maximum transmit power) forthe transmitter 204. The femto node 200 includes a communicationcontroller 210 for managing communications with other nodes and forproviding other related functionality as taught herein. The femto node200 includes one or more data memories 212 for storing variousinformation. The femto node 200 also may include an authorizationcontroller 214 for managing access to other nodes and for providingother related functionality as taught herein. The other componentsillustrated in FIG. 2 are described below.

Sample operations of the system 100 and the femto node 200 will bedescribed in conjunction with the flowcharts of FIGS. 3, 4, 7, 8, and10-11B. For convenience, the operations of FIGS. 3, 4, 7, 8, and 10-11B(or any other operations discussed or taught herein) may be described asbeing performed by specific components (e.g., components of the femtonode 200). It should be appreciated, however, that these operations maybe performed by other types of components and may be performed using adifferent number of components. It also should be appreciated that oneor more of the operations described herein may not be employed in agiven implementation.

Referring initially to FIG. 3, the disclosure relates in some aspects todefining transmit power for a transmitter based on a received signalstrength of a macro node. FIG. 3 illustrates an operation that may beperformed to determine transmit power based on channel conditions suchas the maximum received signal strength from a macro node.

As represented by block 302, in some cases determination of transmitpower for an access node may be invoked due to or may be based on adetermination that a node is in a coverage area of the access node. Forexample, the femto node 200 may elect to recalibrate the femto'stransmit power (e.g., to increase the power) if it determines that ahome access terminal (e.g., a node that is authorized for data access)has entered the femto's coverage area. In addition, the femto node 200may elect to recalibrate its transmit power (e.g., to decrease thepower) if it determines that a visitor access terminal (e.g., that isnot authorized for data access) has entered its coverage area. To thisend, the femto node 200 may include a node detector 224 that maydetermine whether a particular type of node is in a given coverage area.

As represented by block 304, in the event the femto node 200 elects tocalibrate its transmitter (e.g., upon power-up, periodically, or inresponse a trigger such as block 402), the femto node 200 may use, forexample, measurement reports from access terminals to calibrate itsmeasurements of Ecp and Io. To this end, the femto node 200 may includea transmitter calibrator 226 that may receive and act upon measurementreports for adjusting or calibrating the received signal measurements.Furthermore, calibration may rely on received signal strengths invarious forms, for example, in some implementations a received signalstrength determiner 228 may determine a total received signal strengthvalue (e.g., a received signal strength indication, RSSI) from home userequipment for calibration of the measurements of received pilot strength(Ecp) and total received signal strength (Io) by the femto node 200.

As represented by block 306, the femto node 200 (e.g., the transmitpower controller 208) determines a transmit power value (e.g., a maximumvalue) based on the received signal strength. For example, in animplementation where transmit power is based at least in part on areceived signal strength indication, the transmit power may be increasedin response to a decrease in received signal strength at the femtoaccess terminal or if the received signal strength at the femto accessterminal falls below a threshold level. Conversely, the transmit powermay be decreased in response to an increase in the received signalstrength at the femto access terminal or if the received signal strengthat the femto access terminal rises above a threshold level. As aspecific example, if requested DRC over a long time period is alwaysvery high, this may serve an indication that the transmit power valuemay be too high and the femto node 200 may therefore elect to operate atlower transmit power value.

Also, as represented by block 306, the femto node 200 (e.g., thereceived signal strength determiner 228) determines the received signalstrength, such as the pilot strength (e.g., RSCP), of the best macroaccess node on the visitor access terminal's channel (this can be thesame channel as femto or a different channel or both). In other words,the signal strength of the pilot signal having the highest receivedsignal strength is determined at block 306. The received signal strengthdeterminer 228 may determine the received pilot strength in variousways. For example, in some implementations the femto node 200 measuresthe pilot strength (e.g., the receiver 206 monitors the appropriatechannel). In some implementations information relating to the pilotstrength may be received from another node (e.g., a home accessterminal). This information may take the form of, for example, an actualpilot strength measurement (e.g., from a node that measured the signalstrength) or information that may be used to determine a pilot strengthvalue and may be stored in signal strength values 232.

Accordingly, as represented by block 308 in FIG. 3, the femto node 200of FIG. 2 (e.g., the total signal strength determiner 230) determinesthe total received signal strength (e.g., RSSI) on the visitor accessterminal's channel (this can be the same channel as femto or a differentchannel or both). The total signal strength determiner 230 may determinethe signal strength in various ways. For example, in someimplementations the femto node 200 measures the signal strength (e.g.,the receiver 206 monitors the appropriate channel). In someimplementations information relating to the signal strength may bereceived from another node (e.g., a home access terminal) and may bestored in signal strength values 232. This information may take the formof, for example, an actual signal strength measurement (e.g., from anode that measured the signal strength) or information that may be usedto determine a signal strength value.

As represented by block 310, the femto node 200 (e.g., a limitdeterminer 234) may calculate regulatory limits in order to preventworst case errors in calculations and enforce any regulatoryspecifications and may be stored in limit values 236.

The above calculations and determinations are identified herein for aspecific exemplary system. For example, in WCDMA and 1xRTT systems,pilot and control channels are code division multiplexed with trafficand are not transmitted at full power (e.g., Ecp/Io<1.0). Thus, when thefemto node performs the measurements, if neighboring macro cells are notloaded, the total interference signal strength value RSSI_(MACRO) _(—)_(AC) may be lower than a corresponding value for a case wherein theneighboring macro cells are loaded. In one example, considering a worstcase scenario, the femto node may estimate system loading and adjust theRSSI_(MACRO) _(—) _(AC) value to predict the value for a fully loadedsystem.

In the following example, all of the quantities have linear units(instead of dB) and I_(HNB) _(—) _(LINEAR) corresponds to interferencecreated by the femto node at the visitor access terminal. As representedby block 312 of FIG. 3, the femto node 200 (e.g., the transmit powercontroller 208) determines the maximum transmit power based on thereceived signal level of transmissions from the macro node (e.g., macrocell) as received at the femto node 200. As mentioned above, theoperations of FIG. 3 may be used for limiting the coverage hole oneither an adjacent channel or a co-channel.

In some aspects, a femto node may thus convert the determined receivedpower signal level from the femto node 200 into a corresponding allowedtransmit power value. The transmit power may thus be defined in a mannerthat enables operation of a visiting access terminal at a predeterminedminimum distance from a femto node (e.g., corresponding to an edge of acoverage hole), without unduly restricting the operation of the femtonode's home access terminals. Consequently, it may be possible for boththe visiting and home access terminals to operate effectively near theedge of the coverage hole.

As represented by block 314, in some implementations the femto node 200may repeatedly perform any of the above transmit power calibrationoperations (e.g., as opposed to simply determining the transmit power asingle time upon deployment). For example, the femto node 200 may use adefault transmit power value when it is first deployed and may thenperiodically calibrate the transmit power over time. In this case, thefemto node 200 may perform one or more of the operations of FIG. 3(e.g., acquire or receive signal strength or channel qualityinformation) at some other point(s) in time. In some cases, the transmitpower may be adjusted to maintain a desired channel quality over time.In some cases, the operations may be performed on a repeated basis(e.g., daily) so that a femto node may adapt to variations in theenvironment (e.g., a neighbor apartment unit installs a new femto node).In some cases, such a calibration operation may be adapted to mitigatelarge and/or rapid changes in transmit power (e.g., through the use of ahysteresis or filtering technique).

With the above in mind, additional considerations relating to scenarioswhere a macro access terminal (e.g., a visitor access terminal) that isnot associated with a femto node is at or near a coverage area of thefemto node will now be treated. Here, a femto node (e.g., located near awindow) may jam macro access terminals passing by (e.g., on a street) ifthese macro access terminals are not be able to handoff to the femtonode due to a restricted association requirement.

The following parameters will be used in the discussion:

-   Ecp_(MNB) _(—) _(UE): Received pilot strength (RSCP) from the best    macro access node (e.g., MNB) by the macro access terminal (e.g.,    UE) (in linear units).-   Ecp_(MNB) _(—) _(HNB): Received pilot strength (RSCP) from best    macro access node by the femto node (e.g., HNB) (in linear units).-   EC_(HNB) _(—) _(UE): Total received signal strength (RSSI) from the    femto node by the macro access terminal (in linear units). (Also    known as RSSI_(MNB) _(—) _(UE)).

Referring now to FIG. 4, in some implementations the maximum transmitpower defined by the femto node 200 may be constrained based on asignal-to-noise ratio for a home access terminal located around the edgeof a coverage hole. For example, if the signal-to-noise ratio is higherthan expected at a home access terminal that is located where thecoverage hole is expected to end, this means that the coverage hole mayin fact be much larger than desired. As a result, undue interference maybe imposed on visitor access terminals near the intended coverage edge.

The disclosure relates in some aspects to reducing the transmit power ifthe signal-to-noise ratio at the home access terminal is higher thanexpected. The following parameters are used in the discussion thatfollows:

-   Io_(UE): Total received signal strength (Io) by the home access    terminal (e.g., UE) from all access nodes (e.g., NodeBs) in the    absence of the femto node (in linear units).-   Io_(HNB): Total received signal strength (Io) by the home access    terminal from all other access nodes (e.g., macro and femto access    nodes) in the system (in linear units).-   PL_(HNB) _(—) _(edge) Path loss from the femto node (e.g., HNB) to    the home access terminal at the coverage edge (in dB units).

When a femto node is not transmitting, received Ecp/Io by a macro accessterminal may be:

$\begin{matrix}{ {{Ecp}/{Io}} |_{{HNB\_ not}{\_ transmitting}} = \frac{{Ecp}_{MNB\_ UE}}{{Io}_{UE}}} & {{EQUATION}\mspace{14mu} 1}\end{matrix}$

When the femto node is transmitting, received Ecp/Io by the accessterminal may be:

$\begin{matrix}{ {{Ecp}/{Io}} |_{HNB\_ transmitting} = \frac{{Ecp}_{MNB\_ UE}}{{Io}_{UE} + {Ec}_{HNB\_ UE}}} & {{EQUATION}\mspace{14mu} 2}\end{matrix}$

The parameter [Ecp/Io]_(min) is defined as the minimum required Ecp/Iofor the macro access terminal to have proper service (e.g., as discussedabove at FIG. 3). Assuming the macro access terminal is at the edge of afemto node coverage hole and the coverage hole is limited to a certainvalue (e.g., PL_(HNB) _(—) _(edge)=80 dB), then one may impose thefollowing condition for the femto node downlink maximum transmit power:P_(HNB) _(—) _(max) (e.g., to maintain [Ecp/Io]_(min) for a macro accessterminal):

$\begin{matrix}{P_{HNB\_ max} < {\lbrack {( \frac{{Ecp}_{MNB\_ UE}}{\lbrack {{Ecp}/{Io}} \rbrack_{\min}} ) - {Io}_{UE}} \rbrack \cdot 10^{({{PL}_{HNB\_ edge}/10})}}} & {{EQUATION}\mspace{14mu} 3}\end{matrix}$

Similarly, if a home access terminal (e.g., a home UE, HUE) that isserviced by the femto node is located at the edge of the femto coverage,the SNR (the term SINR, e.g., including interference, will be used inthe following discussion) experienced by the home access terminal may bedescribed as:

$\begin{matrix}{{SINR}_{HUE} = \frac{P_{HNB\_ max}}{{Io}_{UE} \cdot 10^{({{PL}_{HNB\_ edge}/10})}}} & {{EQUATION}\mspace{14mu} 4}\end{matrix}$

In some cases Equation 3 may yield to relatively large transmit powerlevels for the femto node which may result in unnecessarily highSINR_(HUE). This may mean, for example, that if a new femto node isinstalled in the vicinity of the old femto node, the new femto node mayend up receiving a high level of interference from the previouslyinstalled femto node. As a result, the newly installed femto node may beconfined to a lower transmit power level and may not provide sufficientSINR for its home access terminals. To prevent this type of effect anSINR cap may be used for the home access terminal at the edge of itshome access terminal coverage as: [SINR]_(max) _(—) _(at) _(—) _(HNB)_(—) _(edge). Thus, one may provide a second constraint for the P_(HNB)_(—) _(max) as:

P_(HNB)_max>[SNR]_(max)_at_HNB_edge·lo_(Ue)·10 ^((PL) ^(HNB)_edge/10)  EQUATION 5

To apply constraints as described in Equations 3 and 5 one may measureEcp_(MNB) _(—UE) and Io_(UE) at the edge of desired HNB coverage(PL_(HNB) _(—) _(edge)). Since professional installation may not bepractical for femto nodes (e.g., due to financial constraints), a femtonode may estimate these quantities by its own measurements of thedownlink channel. For example, the femto node may make measurements:Ecp_(MNB) _(—) _(HNB) and Io_(HNB) to estimate Ecp_(MNB) _(—) _(UE) andIo_(UE) respectively. This scenario is discussed in more detail below inconjunction with Equation 19. Since the femto node location is differentthan the access terminal location there may be some error in thesemeasurements.

In the exemplary embodiment, if the femto node uses its own measurementsfor adaptation of its own transmit power, this error could result inlower or higher transmit power values compared to optimum. As apractical method to prevent worst cases errors, certain upper and lowerlimits may be enforced on P_(HNB) _(—) _(max) as P_(HNB) _(—) _(max)_(—) _(limit) and P_(HNB) _(—) _(min) _(—) _(limit) (e.g., as discussedabove).

In view of the above, referring to block 402 FIG. 4, a transmit poweradjustment algorithm may thus involve identifying a home access terminalnear a coverage edge of a femto node. In the example of FIG. 2, thisoperation may be performed by the node detector 224. In someimplementations, the position of the home access terminal may bedetermined based on path loss measurements between the home accessterminal and the femto node (e.g., as discussed herein).

At block 404, the femto node 200 (e.g., an SNR determiner 242) maydetermine SNR values (e.g., SINR) associated with the home accessterminal. In some cases, this may involve receiving SNR information fromthe home access terminal (e.g., in a channel quality report or ameasurement report). For example, the home access terminal may sendmeasured RSSI information or calculated SNR information to the femtonode 200. In some cases, CQI information provided by the home accessterminal may be correlated (e.g., by a known relationship) to an SNRvalue of the home access terminal. Thus, the femto node 200 may deriveSNR from received channel quality information.

As mentioned above, determining an SNR value may involve the femto node200 autonomously calculating the SNR value as discussed herein. Forexample, in cases where the femto node 200 performs the measurementoperations on its own, the femto node 200 may initially measure:

-   Ecp_(MNB) _(—) _(HNB): Total received pilot strength from best macro    access node by the femto node.-   Io_(HNB): Total received signal strength (Io) by the femto node from    all other access nodes (e.g., macro and femto nodes) in the system.

The femto node 200 may then determine upper power limits:

$\begin{matrix}{P_{{HNB\_ max}\_ 1} = {\lbrack {( \frac{{Ecp}_{MNB\_ HNB}}{\lbrack {{Ecp}/{Io}} \rbrack_{\min}} ) - {Io}_{HNB}} \rbrack \cdot 10^{({{PL}_{HNB\_ edge}/10})}}} & {{EQUATION}\mspace{14mu} 6} \\{P_{{HNB\_ max}\_ 2} = {\lbrack{SINR}\rbrack_{{max\_ at}{\_ HNB}{\_ edge}} \cdot {Io}_{HNB} \cdot 10^{({{PL}_{HNB\_ edge}/10})}}} & {{EQUATION}\mspace{14mu} 7}\end{matrix}$

Here, Equation 6 relates to the maximum transmit power determined in asimilar manner as discussed in FIG. 3 and Equation 7 relates todetermining another maximum limit for the transmit power based on SNR.It may be observed that Equation 6 is similar to Equation 3 except thatIo is measured at the femto node. Thus, Equation 6 ensures that theEcp/Io of a macro access terminal at the home node B coverage edge doesnot fall below the minimum Ecp/Io. In both of these equations, thedetermined transmit power is based on signals received at the femto nodeand on the path loss to the coverage edge (e.g., based on the distanceto the edge).

At block 406 of FIG. 4, the femto node 200 (e.g., the transmit powercontroller 208) may determine the transmit power based on the maximumsdefined by Equations 6 and 7. In addition, as mentioned above the finalmaximum power value may be constrained by absolute minimum and maximumvalues:

P _(HNB) _(—) _(total)=max└P _(HNB) _(—) _(min) _(—) _(limit),min(P_(HNB) _(—) _(max) _(—) ₁ ,P _(HNB) _(—) _(max) _(—) ₂ ,P _(HNB) _(—)_(max) _(—) _(limit))┘  EQUATION 8

As an example of Equation 8, PL_(HNB) _(—) _(edge) may be specified tobe 80 dB, P_(HNB) _(—) _(max) _(—) _(limit) may be specified to be 20dBm, P_(HNB) _(—) _(min) _(—) _(limit) may be specified to be −10 dBm,and [SINR]_(max) _(—) _(at) _(—) _(HNB) _(—) _(edge) and [Ecp/Io]_(min)may depend on the particular air interface technology in use.

As mentioned above, the teachings herein may be implemented in awireless network that includes macro coverage areas and femto coverageareas. FIG. 5 illustrates an example of a coverage map 500 for a networkwhere several tracking areas 502 (or routing areas or location areas)are defined. Specifically, areas of coverage associated with trackingareas 502A, 502B, and 502C are delineated by the wide lines in FIG. 5.

The system provides wireless communication via multiple cells 504(represented by the hexagons), such as, for example, macro cells 504Aand 504B, with each cell being serviced by a corresponding access node506 (e.g., access nodes 506A-506C). As shown in FIG. 5, access terminals508 (e.g., access terminals 508A and 508B) may be dispersed at variouslocations throughout the network at a given point in time. Each accessterminal 508 may communicate with one or more access nodes 506 on aforward link (“FL”) and/or a reverse link (“RL) at a given moment,depending upon whether the access terminal 508 is active and whether itis in soft handoff, for example. The network may provide service over alarge geographic region. For example, the macro cells 504 may coverseveral blocks in a neighborhood. To reduce the complexity of FIG. 5,only a few access nodes, access terminals, and femto nodes are shown.

The tracking areas 502 also include femto coverage areas 510. In thisexample, each of the femto coverage areas 510 (e.g., femto coverage area510A) is depicted within a macro coverage area 504 (e.g., macro coveragearea 504B). It should be appreciated, however, that a femto coveragearea 510 may not lie entirely within a macro coverage area 504. Inpractice, a large number of femto coverage areas 510 may be defined witha given tracking area 502 or macro coverage area 504. Also, one or morepico coverage areas (not shown) may be defined within a given trackingarea 502 or macro coverage area 504. To reduce the complexity of FIG. 5,only a few access nodes 506, access terminals 508, and femto nodes 510are shown.

FIG. 6 illustrates a network 600 where femto nodes 602 are deployed inan apartment building. Specifically, a femto node 602A is deployed inapartment 1 and a femto node 602B is deployed in apartment 2 in thisexample. The femto node 602A is the home femto for an access terminal604A. The femto node 602B is the home femto for an access terminal 604B.

As illustrated in FIG. 6, for the case where the femto nodes 602A and602B are restricted, each access terminal 604 may only be served by itsassociated (e.g., home) femto node 602. In some cases, however,restricted association may result in negative geometry situations andoutages of femto nodes. For example, in FIG. 6 the femto node 602A iscloser to the access terminal 604B than the femto node 602B and maytherefore provide a stronger signal at the access terminal 604B. As aresult, the femto node 602A may unduly interfere with reception at theaccess terminal 604B. Such a situation may thus affect the coverageradius around the femto node 602B at which an associated access terminal604 may initially acquire the system and remain connected to the system.

Referring now to FIGS. 7-11B, the disclosure relates in some aspects toadaptively adjusting transmit power (e.g., maximum downlink transmitpower) of neighboring access nodes to mitigate scenarios of negativegeometries. For example, as mentioned above maximum transmit power maybe defined for overhead channels that are then transmitted as theirdefault fraction of the maximum access node transmit power. Forillustration purposes, the following describes a scenario where transmitpower of a femto node is controlled based on a measurement reportgenerated by an access terminal associated with a neighboring femtonode. It should be appreciated, however, that the teachings herein maybe applied to other types of nodes.

Transmit power control as taught herein may be implemented through adistributed power control scheme implemented at the femto nodes and/orthrough the use of a centralized power controller. In the former case,adjustments of transmit power may be accomplished through the use ofsignaling between neighboring femto nodes (e.g., femto nodes associatedwith the same operator). Such signaling may be accomplished, forexample, through the use of upper layer signaling (e.g., via thebackhaul) or appropriate radio components. In the latter case mentionedabove, adjustments to transmit power of a given femto node may beaccomplished via signaling between femto nodes and a centralized powercontroller.

The femto nodes and/or the centralized power controller may utilizemeasurements reported by access terminals and evaluate one or morecoverage criteria to determine whether to send a request to a femto nodeto reduce transmit power. A femto node that receives such a request mayrespond by lowering its transmit power if it is able to maintain itscoverage radius and if its associated access terminals would remain ingood geometry conditions.

FIG. 7 describes several operations relating to an implementation whereneighboring femto nodes may cooperate to control one another's transmitpower. Here, various criteria may be employed to determine whethertransmit power of a neighbor node should be adjusted. For example, insome aspects a power control algorithm may attempt to maintain aparticular coverage radius around the femto node (e.g., a certain CPICHEcp/Io is maintained a certain path loss away from the femto node). Insome aspects a power control algorithm may attempt to maintain a certainquality of service (e.g., throughput) at an access terminal. Initially,the operations of FIGS. 7 and 8 will be described in the context of theformer algorithm.

As represented by block 702 of FIG. 7, a given femto node initially setits transmit power to defined value. For example, all of the femto nodesin the system may initially set their respective transmit power to themaximum transmit power that still mitigates the introduction of coverageholes in a macro coverage area. As a specific example, the transmitpower for a femto node may be set so that the CPICH Ecp/Io of a macroaccess terminal at a certain path loss away (e.g. 80 dB) from the femtonode is above a certain threshold (e.g. −18 dB). In someimplementations, the femto nodes may employ one or more of thealgorithms described above in conjunction with FIGS. 2-4 to establish amaximum transmit power value.

As represented by block 704, each access terminal in the network (e.g.,each access terminal associated with a femto node) may measure thesignal strength of signals that it receives in its operating band. Eachaccess terminal may then generate a neighbor report including, forexample, the CPICH RSCP (pilot strength) of its femto node, the CPICHRSCP of all femto nodes in its neighbor list, and the RSSI of theoperating band.

In some aspects, each access terminal may perform this operation inresponse to a request from its home femto node. For example, a givenfemto node may maintain a list of neighboring femto nodes that it sendsto its home access terminals. This neighbor list may be supplied to thefemto node by an upper layer process or the femto node may populate thelist on its own by monitoring downlink traffic (provided the femto nodeincludes appropriate circuitry to do so). The femto node may repeatedly(e.g., periodically) send a request to its home access terminals for theneighbor report.

As represented by blocks 706 and 708, the femto node (e.g., the transmitpower controller 208 of FIG. 2) determines whether signal reception ateach of its home access terminals is acceptable. For example, for animplementation that seeks to maintain a particular coverage radius, agiven femto node “i” (e.g., home nodeB, “HNB”) may estimate the CPICHEcp/Io_i of a given associated access terminal “i” (e.g., home userequipment, “HUE”) assuming the access terminal “i” is a certain pathloss (PL) away from the femto node “i” (e.g., assuming the locationmeasured by the femto node “i” will not change much). Here Ecp/Io_i forthe access terminal “i” is

$\begin{matrix}{{{Ecp}/{Io\_ i}} = {\frac{{Ecp}_{{HNB\_ HUE}{\_ i}}}{{Io}_{HUE\_ i}}.}} & {{EQUATION}\mspace{14mu} 9}\end{matrix}$

In some implementations, a femto node (e.g., the signal strengthdeterminer 226) may determine RSSI on behalf of its home accessterminals. For example, the femto node may determine RSSI for an accessterminal based on the RSCP values reported by an access terminal. Insuch a case, the access terminal need not send an RSSI value in theneighbor report. In some implementations, a femto node may determine(e.g., estimate) RSSI and/or RSCP on behalf of its home accessterminals. For example, the signal strength determiner 226 may measureRSSI at the femto node and the received pilot strength determiner 228may measure RSCP at the femto node.

The femto node “i” may determine whether Ecp/Io_i is less than or equalto a threshold to determine whether coverage for the access terminal “i”is acceptable. If coverage is acceptable, the operational flow mayreturn back to block 704 where the femto node “i” waits to receive thenext neighbor report. In this way, the femto node may repeatedly monitorconditions at its home access terminals over time.

If coverage is not acceptable at block 708, the femto node “i” maycommence operations to adjust the transmit power of one or moreneighboring femto nodes. Initially, as represented by block 710, thefemto node “i” may set its transmit power to the maximum allowed value(e.g., the maximum value discussed at block 702). Here, the transmitpower of the femto node “i” may have been reduced after it was set themaximum value at block 702, for example, if the femto node “i” hadobeyed an intervening request from a neighboring femto node to reduceits transmit power. In some implementations, after increasing thetransmit power, the femto node “i” may determine whether the coveragefor the access terminal “i” is now acceptable. If so, the operationalflow may return back to block 704 as discussed above. If not, theoperational flow may proceed to block 712 as discussed below. In someimplementations the femto node “i” may perform the following operationswithout checking the effect of block 710.

As represented by block 712, the femto node “i” (e.g., the transmitpower controller 208) may rank the femto nodes in the neighbor report bythe strength of their corresponding RSCPs as measured by the accessterminal. A ranked list of the potentially interfering nodes 246 maythen be stored in the data memory 212. As will be discussed below, theoperational block 712 may exclude any neighboring femto node that hassent a NACK in response to a request to reduce transmit power and wherea timer associated with that NACK has not yet expired.

As represented by block 714, the femto node “i” (e.g., the transmitpower controller 208) selects the strongest interfering neighboringfemto node (e.g., femto node “j”) and determines by how much that femtonode should reduce its transmit power to maintain a given Ecp/Io foraccess terminal “i” at the designated coverage radius (path loss). Insome aspects the amount (e.g., percentage) of power reduction may berepresented by a parameter alpha_p. In some aspects, the operations ofblock 714 may involve determining whether Ecp/Io_i is greater than orequal to a threshold as discussed above.

Next, the femto node “i” (e.g., the transmitter 204 and thecommunication controller 210) sends a message to the femto node “j”requesting it to lower its power by the designated amount (e.g.,alpha_p). Sample operations that the femto node “j” may perform uponreceipt of such request are described below in conjunction with FIG. 8.

As represented by block 716, the femto node “i” (e.g., the receiver 206and the communication controller 210) will receive a message from thefemto node “j” in response to the request of block 714. In the event thefemto node “j” elected to reduce its transmit power by the requestedamount, the femto node “j” will respond to the request with anacknowledgment (ACK). In this case, the operational flow may return toblock 704 as described above.

In the event the femto node “j” elected to not reduce its transmit powerby the requested amount, the femto node “j” will respond to the requestwith a negative acknowledgment (NACK). In its response, the femto node“j” may indicate that it did not reduce its power at all or that itreduced its power by a given amount less than the requested amount. Inthis case, the operational flow may return to block 712 where the femtonode “i” may re-rank the femto nodes in the neighbor report according tothe RSCP measured by the access terminal “i” (e.g., based on a newlyreceived neighbor report). Here, however, the femto node “j” will beexcluded from this ranking as long as the timer associated with its NACKhas not expired. The operations of blocks 712 through 718 may thus berepeated until the femto node “i” determines that the Ecp/Io for theaccess terminal “i” is at the target value or has improved as much aspossible.

FIG. 8 illustrates sample operations that may be performed by a femtonode that receives a request to reduce transmit power. The receipt ofsuch a request is represented by block 802. In an implementation wherethe node 200 of FIG. 2 is also capable of performing these operations,the operations of block 802 may be performed at least in part by thereceiver 206 and the communication controller 210, the operations ofblocks 804-808 and 812-814 may be performed at least in part by thetransmit power controller 208, and the operations of blocks 810 may beperformed at least in part by the transmitter 204 and the communicationcontroller 210.

At blocks 804 and 806, the femto node determines whether coverage forone or more home access terminals will be acceptable if the transmitpower is adjusted as requested. For example, the femto node “j” mayevaluate a request to lower its transmit power to alpha_p*HNB_Tx_j bydetermining whether each of its access terminals may pass a test similarto the test of described at block 706. Here, the femto node “j” maydetermine whether the Ecp/Io of an associated access terminal at adesignated coverage radius is greater than or equal to a thresholdvalue.

If coverage is acceptable at block 806, the femto node “j” reduces itstransmit power by the requested amount for a defined period of time(block 808). At block 810, the femto node “j” responds to the requestwith an ACK. The operational flow may then return to block 802 wherebythe femto node processes any additional requests to reduce transmitpower as they are received.

If coverage is not acceptable at block 806, the femto node “j”determines how much it may lower its transmit power such that the testof block 804 passes (block 812). Here, it should be appreciated that insome cases the femto node “j” may elect to not reduce its transmit powerat all.

At block 814, the femto node “j” reduces its transmit power by theamount determined at block 812, if applicable, for a defined period oftime. This amount may be represented by, for example, the valuebeta_p*HNB_Tx_j.

At block 816, the femto node “j” will then respond to the request with anegative acknowledgment (NACK). In its response, the femto node “j” mayindicate that it did not reduce its power at all or that it reduced itspower by a given amount (e.g., beta_p*HNB_Tx_j). The operational flowmay then return to block 802 as described above.

In some implementations, the femto node “i” and the femto node “j”maintain respective timers that count for a defined period time inconjunction with an ACK or a NACK. Here, after its timer expires, thefemto node “j” may reset its transmit power back to the previous level.In this way, the femto node “j” may avoid being penalized in the eventthe femto node “i” has moved.

Also, in some cases each femto node in the network may store themeasurements (e.g., the neighbor reports) that it received from anaccess terminal the last time the access terminal connected with thefemto node. In this way, in the event no access terminals are currentlyconnected to the femto node, the femto node may calculate a minimumtransmit power to ensure Ecp/Io coverage for initial acquisition.

If the femto node has sent requests to all neighboring femto nodes toreduce their power and cannot yet maintain the desired coverage at thespecified coverage radius, the femto node may calculate how much itscommon pilot Ec/Ior needs to be increased above its default level toreach the target coverage. The femto node may then raise the fraction ofits pilot power accordingly (e.g., within a preset maximum value).

An implementation that utilizes a scheme such as the one described aboveto maintain a coverage radius may thus be used to effectively settransmit power values in a network. For example, such a scheme may set alower bound on the geometry (and throughput) an access terminal willhave if it is within the designated coverage radius. Moreover, such ascheme may result in power profiles being more static whereby a powerprofile may only change when a femto node is added to or removed fromthe network. In some implementations, to eliminate further CPICH outagethe above scheme may be modified such that the CPICH Ec/Ior is adaptedaccording to measurements collected at the femto node.

A given femto node may perform the operations of blocks 704-718 for allof its associated access terminals. If more than one access terminal isassociated with a femto node, the femto node may send a request to aninterfering femto node whenever any one of its associated accessterminals is being interfered with.

Similarly when evaluating whether or not to respond to a request toreduce transmit power, a femto node performs the test of block 804 forall its associated access terminals. The femto node may then select theminimum power that will guarantee an acceptable performance to all itsassociated access terminals.

In addition, each femto node in the network may perform these operationsfor its respective access terminals. Hence, each node in the network maysend a request to a neighboring node to reduce transmit power or mayreceive a request from a neighboring node to reduce transmit power. Thefemto nodes may perform these operations in an asynchronous manner withrespect to one another.

As mentioned above, in some implementations a quality of servicecriterion (e.g., throughput) may be employed to determine whether toreduce transmit power of a femto node. Such a scheme may be employed inaddition to or instead of the above scheme.

In a similar manner as discussed above, RSCP_i_j is defined as the CPICHRSCP of femto node “j” (HNB_J) as measured by access terminal “i”(HUE_i). RSSI_i is the RSSI as measured by access terminal “i.” Ecp/Io_iand Ecp/Nt_i, respectively, are the CPICH Ecp/Io and the CPICH SINR(signal to interference and noise ratio) of access terminal “i” from itsassociated femto node “i” (HNB_i). The femto node calculates thefollowing:

$\begin{matrix}{( {{Ecp}/{Io\_ i}} ) = \frac{RSCP\_ i}{RSSI\_ i}} & {{EQUATION}\mspace{14mu} 10} \\{{SINR\_ i}\; = \frac{{RSCP\_ i}/( {{Ecp}/{Ior}} )}{{RSSI\_ i} - {{RSCP\_ i}/( {{Ecp}/{Ior}} )}}} & {{EQUATION}\mspace{14mu} 11}\end{matrix}$

where Ecp/Ior is the ratio of the CPICH pilot transmit power to thetotal power of the cell.

The femto node estimates the Ecp/Io of the home access terminal if itwere at the edge of the femto node coverage corresponding to a path lossof PL_(HNB) _(—) _(Coverage):

$\begin{matrix}{( {{Ecp}/{Io\_ i}} )_{HNB\_ Coverage} = \frac{{RSCP\_ i}{\_ i}_{HNB\_ Coverage}}{RSSI\_ i}} & {{EQUATION}\mspace{14mu} 12}\end{matrix}$

where RSCP_i_i_(HNB) _(—) _(Coverage) is the received pilot strength ataccess terminal “i” from its own femto node “i” at the edge of the femtonode “i” coverage. The edge of coverage corresponds to a path loss (PL)from the femto node equal PL_(HNB) _(—) _(Coverage) and

RSCP _(—) i _(—) i _(HNB) _(—) _(Coverage) =HNB _(—) Tx _(—)i*(Ecp/Ior)/PL _(HNB) _(—) _(Coverage)  EQUATION 13

Let (Ecp/Io)_Trgt_A be a threshold on the CPICH Ecp/Io preconfigured inthe femto node. The femto node checks the following:

(Ecp/Io _(—) i)_(HNB) _(—) _(coverage)>(Ecp/Io)_(—) Trgt _(—)A?  EQUATION 14

If the answer is YES, the femto node does not send a request to reducetransmit power. If the answer is NO, the femto node sends a request toreduce transmit power as described below. In addition, or alternatively,the femto node may perform a similar test relating to throughput (e.g.,SINR_i).

The femto node sets its power to the maximum allowed by the macro cellcoverage hole condition. The femto node “i” ranks the neighbor cells indescending order of the home access terminal's reported RSCP. The femtonode “i” picks the neighbor cell femto node “j” with the highest RSCPvalue, RSCP_i_j.

The serving femto node “i” calculates how much femto node “j” needs tolower its transmit power such that the performance of its accessterminal “i” improves. Let (Ecp/Io)_Trgt_A be a target CPICH Ecp/Io forthe home access terminal that is preconfigured in the femto node. Thistarget Ecp/Io can be chosen such that home access terminals are not inoutage. It can also be more aggressive to guarantee a minimum geometryof the home access terminals to maintain a certain data throughput orperformance criteria. The desired RSCP_i_j_trgt seen by access terminal“i” from neighbor femto node “j” to maintain (Ecp/Io)_Trgt_A may becalculated as:

$\begin{matrix}{{{RSCP\_ i}{\_ j}{\_ Trgt}} = {\frac{( {{Ecp}/{Ior}} )*{RSCP\_ i}{\_ i}_{HNB\_ Coverage}}{( {{Ecp}/{Io}} ){\_ Trgt}{\_ A}} - {( {{Ecp}/{Ior}} )*{RSSI\_ i}} + {{RSCP\_ i}{\_ j}}}} & {{EQUATION}\mspace{14mu} 15}\end{matrix}$

In addition, or alternatively, the femto node may perform a similar testrelating to throughput. The femto node “i” calculates the ratioalpha_p_j by which femto node “j” should lower its power as:

alpha_(—) p _(—) j=RSCP _(—) i _(—) j _(—) Trgt/RSCP _(—) i _(—)j  EQUATION 16

The femto node “i” sends a request to femto node “j” to lower itstransmit power by a ratio alpha_p_j. As discussed herein this requestmay be sent through upper layer signaling (backhaul) to a centralizedalgorithm or sent to femto node “j” directly from femto node “i.”

The femto node “j” evaluates whether it may respond to the request offemto node “i” by making its transmit powerHNB_Tx_new_j=alpha_p_j*HNB_Tx_j, where HNB_Tx_j is set as above. In someimplementations the femto node “j” checks two tests.

Test 1: This test is based on the scheme previously described for FIG.7. The CPICH Ecp/Io of an associated home access terminal, which is awayfrom the femto node “j” by the coverage radius, is above a certainthreshold (Ecp/Io)_Trgt_B. This test is to guarantee that its own UEhave an acceptable performance within a certain radius around the femtonode and another registered home access terminal can also acquire thefemto node. This is calculated as follows:

$\begin{matrix}{( {{Ecp}/{Io\_ j}} )_{HNB\_ Coverage} = \frac{{RSCP\_ j}{\_ j}_{HNB\_ Coverage}}{RSSI\_ j}} & {{EQUATION}\mspace{14mu} 17}\end{matrix}$

where RSSI_J and RSCP_j_j are the RSSI and RSCP reported by HUE_j at thecoverage radius (or otherwise estimated by HNB_j) to femto node “j”before transmit power modification. The test is

(Ecp/Io _(—) j)_(HNB) _(—) _(coverage)>(Ecp/Io)_(—) Trgt _(—)B?  EQUATION 18

Test 2: The CPICH SINR of HUE_j is greater than a certain target tomaintain a certain performance criterion (e.g., quality of service suchas throughput):

SINR_new_(—) j>SINR_(—) Trgt?  EQUATION 19

where

$\begin{matrix}{{{SINR\_ new}{\_ j}} = \frac{{alpha\_ p}{\_ j}*{RSCP\_ j}{\_ j}}{{RSSI\_ j} - {{RSCP\_ j}{{\_ j}/( {{Ecp}/{Ior}} )}}}} & {{EQUATION}\mspace{14mu} 20}\end{matrix}$

If either or both tests pass (depending on the particularimplementation), femto node “j” lowers its transmit power to bealpha_p_j*HNB_Tx_j and sends an ACK to femto node “i”, given that thenew power is above the minimum allowed (e.g. −20 dBm).

If one or both tests fail, femto node “j” does not lower its transmitpower to the required value. Instead, it calculates how much it canlower its transmit power without hurting its performance. In otherwords, in an implementation that uses both tests, the femto node maycalculate its new transmit powers such that both Test 1 and Test 2 passand lowers its transmit power to the higher of the two. However, if withthe current femto node “j” power settings either test fails, then femtonode “j” does not lower its power. The femto nodes may also lower theirpower to a minimum standardized limit (e.g., as discussed herein). Inall these cases, femto node “j” may report a NACK to femto node “i” withits final power settings.

The algorithms discussed above allow femto nodes to adaptively adjusttheir transmit powers in a collaborative fashion. These algorithm havemany parameters which can be adjusted (e.g., by an operator) such as,for example, Ecp/Io_Trgt_A, Coverage_radius, Ecp/Io_Trgt_B, SINR_Trgt,and the timers. The algorithms may be further refined by making thethresholds adapted by a learning process.

In some aspects, the timers may be varied (e.g., independently) tooptimize system performance. If an access terminal “i” is not connectedto a femto node “i,” and femto node “j” is already transmitting toaccess terminal “j,” access terminal “i” may not be able to acquirefemto node “i” due to its low CPICH Ecp/Io. The above algorithm may thenbe modified such that each femto node tries to maintain a minimum CPICHEcp/Io within a certain radius around the femto node. A disadvantage ofthis is that neighbor access terminal “j” may be penalized while femtonode “i” has no access terminal associated with it. To avoidcontinuously penalizing neighbor femto nodes, femto node “i” will sendin its request to neighbor femto node “j” an indication that thisrequest is for initial acquisition. If femto node “j” responds bylowering its power, it sets a timer and femto node “i” sets a largertimer. The femto node “j” will reset its transmit power to its defaultvalue after its timer expires but femto node “i” will not send anotherrequest (for initial acquisition) to femto node “j” until the timer forfemto node “i” expires. An issue remains in that femto node “i” may haveto estimate the RSSI_i as there is not an access terminal associatedwith it. The femto node “i” also may have to estimate the neighboringinterferers RSCP_j. However, the strongest interferers the femto nodessee are not necessarily the strongest interferers its access terminalswill see.

To alleviate the initial acquisition problem, access terminals may alsobe allowed to camp in idle mode on neighboring femto nodes with the samePLMN_ID. The access terminals may read the neighbor list on the campedfemto node which may contain the scrambling code and timing of its ownfemto node. This can put the access terminal at an advantage whenacquiring its femto node at negative geometries.

Referring now to FIGS. 9-11B, implementations that employ a centralizedpower controller to control the transmit power of femto nodes aredescribed. FIG. 9 illustrates a sample system 900 including acentralized controller 902, femto nodes 904, and access terminals 906.Here, femto node 904A is associated with access terminal 906A and femtonode 904B is associated with access terminal 906B. The centralized powercontroller 902 includes a transceiver 910 (with transmitter 912 andreceiver 914 components) as well as a transmit power controller 916. Insome aspects, these components may provide functionality similar to thefunctionality of the similarly named components of FIG. 2.

FIG. 10 describes various operations that may be performed in animplementation where a femto node (e.g., femto node 904A) simplyforwards the neighbor list information it receives from its associatedaccess terminal (e.g., access terminal 906A) to the centralized powercontroller 902. The centralized power controller 902 may then performoperations similar to those described above to request a femto node(e.g., femto node 904B) that is in the vicinity of the femto node 904Ato reduce its transmit power.

The operations blocks 1002 and 1004 may be similar to the operations ofblocks 702 and 704 discussed above. At block 1006, the femto node 904Aforwards a neighbor list 908A it receives from the access terminal 906Ato the centralized power controller 902. The operations of blocks1002-1006 may be repeated on a regular basis (e.g., periodically)whenever the femto node 904A receives a neighbor report from the accessterminal 906A.

As represented by block 1008, the centralized power controller 902 mayreceive similar information from other femto nodes in the network. Atblock 1010, the centralized power controller 902 may then performoperations similar to those discussed above (e.g., at block 706) todetermine whether a femto node should reduce its transmit power. In someaspects, the centralized power controller 902 may make a power controldecision based on information it receives relating to conditions atmultiple femto nodes. For example, if a given femto node is interferingwith several other femto nodes, the centralized power controller 902 mayattempt to reduce the power of that femto node first.

At block 1012, the centralized power controller 902 sends a message toeach femto node that the centralized controller 900 determines shouldreduce its transmit power. As above, this request may indicate thedegree to which a designated femto node should reduce its power. Theseoperations may be similar to the operations of blocks 712 and 714.

The centralized power controller 902 receives responses from the femtonodes at block 1014. As represented by block 1016, if no NACKs arereceived in response to the requests issued at block 1012, theoperational flow for the centralized power controller 902 returns toblock 1008 where the centralized controller 902 continues to receiveinformation from the femto nodes in the network and performs the powercontrol operations described above.

If, on the other hand, one or more NACKs are received in response to therequests issued at block 1012, the operational flow for the centralizedpower controller 902 returns to block 1010 where the centralizedcontroller 902 may identify other femto nodes that should reduce theirtransmit power and then sends out new power control messages. Again,these operations may be similar to blocks 712 and 714 discussed above.

FIGS. 11A and 11B describe various operations that may be performed inan implementation where a femto node (e.g., femto node 904A) identifiesa neighboring femto node (e.g., femto node 904B) that should reduce itspower and sends this information to the centralized power controller902. The centralized power controller 902 may then send a request to thefemto node 904B to reduce its transmit power.

The operations blocks 1102-1112 may be similar to the operations ofblocks 702-712 discussed above. At block 1114, the femto node 904A sendsa message identifying the femto node 904B to the centralized powercontroller 902. Such a message may take various forms. For example, themessage may simply identify a single femto node (e.g., femto node 904B)or the message may comprise a ranking of femto nodes (e.g., as describedabove at block 712). Such a list also may include some or all of theneighbor report the femto node 904A received from the access terminal906A. The operations of blocks 1102-1114 may be repeated on a regularbasis (e.g., periodically) whenever the femto node 904A receives aneighbor report from the access terminal 906A.

As represented by block 1116, the centralized power controller 902 mayreceive similar information from other femto nodes in the network. Atblock 1118, the centralized power controller 902 may determine whetherit should make any adjustments to any requests for reduction in transmitpower it receives (e.g., based on other requests it receives requestinga reduction in power for the same femto node).

At block 1120, the centralized power controller 902 may then send amessage to each femto node that the centralized controller 902determines should to reduce its power. As above, this request mayindicate the degree to which the designated femto node should reduce itspower.

The centralized power controller 902 receives responses from the femtonodes at block 1122. As represented by block 1124, if no NACKs arereceived in response to the requests issued at block 1120, theoperational flow for the centralized power controller 902 returns toblock 1116 where the centralized controller 902 continues to receiveinformation from the femto nodes in the network and performs the powercontrol operations described above.

If, on the other hand, one or more NACKs are received in response to therequests issued at block 1120, the operational flow for the centralizedpower controller 902 returns to block 1118 where the centralizedcontroller 902 may identify other femto nodes that should reduce theirtransmit power and then sends out new power control messages (e.g.,based on a ranked list received from the femto node 904A).

In view of the above it should be appreciated that the teachings hereinmay provide an effective way of managing transmit power of neighboringaccess nodes. For example, in a static environment downlink transmitpowers of the femto nodes may be adjusted to a static value wherebyservice requirements at all access terminals may be satisfied.Consequently, such a solution to be compatible with legacy accessterminals since all channels may continuously be transmitted at constantpowers. In addition, in a dynamic environment transmit powers may bedynamically adjusted to accommodate the changing service requirements ofthe nodes in the system.

Connectivity for a femto node environment may be established in variousways. For example, FIG. 12 illustrates an exemplary communication system1200 where one or more femto nodes are deployed within a networkenvironment. Specifically, the system 1200 includes multiple femto nodes1210 (e.g., femto nodes 1210A and 1210B) installed in a relatively smallscale network environment (e.g., in one or more user residences 1230).Each femto node 1210 may be coupled to a wide area network 1240 (e.g.,the Internet) and a mobile operator core network 1250 via a DSL router,a cable modem, a wireless link, or other connectivity means (not shown).As discussed herein, each femto node 1210 may be configured to serveassociated access terminals 1220 (e.g., access terminal 1220A) and,optionally, other access terminals 1220 (e.g., access terminal 1220B).In other words, access to femto nodes 1210 may be restricted whereby agiven access terminal 1220 may be served by a set of designated (e.g.,home) femto node(s) 1210 but may not be served by any non-designatedfemto nodes 1210 (e.g., a neighbor's femto node 1210).

The owner of a femto node 1210 may subscribe to mobile service, such as,for example, 3G mobile service offered through the mobile operator corenetwork 1250. In addition, an access terminal 1220 may be capable ofoperating both in macro environments and in smaller scale (e.g.,residential) network environments. In other words, depending on thecurrent location of the access terminal 1220, the access terminal 1220may be served by an access node 1260 of the macro cell mobile network1250 or by any one of a set of femto nodes 1210 (e.g., the femto nodes1210A and 1210B that reside within a corresponding user residence 1230).For example, when a subscriber is outside his home, he is served by astandard macro access node (e.g., node 1260) and when the subscriber isat home, he is served by a femto node (e.g., node 1210A). Here, itshould be appreciated that a femto node 1210 may be backward compatiblewith existing access terminals 1220.

A femto node 1210 may be deployed on a single frequency or, in thealternative, on multiple frequencies. Depending on the particularconfiguration, the single frequency or one or more of the multiplefrequencies may overlap with one or more frequencies used by a macronode (e.g., node 1260).

An access terminal 1220 may be configured to communicate either with themacro network 1250 or the femto nodes 1210, but not both simultaneously.In addition, an access terminal 1220 being served by a femto node 1210may not be in a soft handover state with the macro network 1250.

In some aspects, an access terminal 1220 may be configured to connect toa preferred femto node (e.g., the home femto node of the access terminal1220) whenever such connectivity is possible. For example, whenever theaccess terminal 1220 is within the user's residence 1230, it may bedesired that the access terminal 1220 communicate only with the homefemto node 1210.

In some aspects, if the access terminal 1220 operates within the macrocellular network 1250 but is not residing on its most preferred network(e.g., as defined in a preferred roaming list), the access terminal 1220may continue to search for the most preferred network (e.g., thepreferred femto node 1210) using a Better System Reselection (“BSR”),which may involve a periodic scanning of available systems to determinewhether better systems are currently available, and subsequent effortsto associate with such preferred systems. With the acquisition entry,the access terminal 1220 may limit the search for specific band andchannel. For example, the search for the most preferred system may berepeated periodically. Upon discovery of a preferred femto node 1210,the access terminal 1220 selects the femto node 1210 for camping withinits coverage area.

The teachings herein may be employed in a wireless multiple-accesscommunication system that simultaneously supports communication formultiple wireless access terminals. As mentioned above, each terminalmay communicate with one or more base stations via transmissions on theforward and reverse links. The forward link (or downlink) refers to thecommunication link from the base stations to the terminals, and thereverse link (or uplink) refers to the communication link from theterminals to the base stations. This communication link may beestablished via a single-in-single-out system, amultiple-in-multiple-out (“MIMO”) system, or some other type of system.

A MIMO system employs multiple (N_(T)) transmit antennas and multiple(N_(R)) receive antennas for data transmission. A MIMO channel formed bythe N_(T) transmit and N_(R) receive antennas may be decomposed intoN_(S) independent channels, which are also referred to as spatialchannels, where N_(S)≦min{N_(T), N_(R)}. Each of the N_(S) independentchannels corresponds to a dimension. The MIMO system may provideimproved performance (e.g., higher throughput and/or greaterreliability) if the additional dimensionalities created by the multipletransmit and receive antennas are utilized.

A MIMO system may support time division duplex (“TDD”) and frequencydivision duplex (“FDD”). In a TDD system, the forward and reverse linktransmissions are on the same frequency region so that the reciprocityprinciple allows the estimation of the forward link channel from thereverse link channel. This enables the access point to extract transmitbeam-forming gain on the forward link when multiple antennas areavailable at the access point.

The teachings herein may be incorporated into a node (e.g., a device)employing various components for communicating with at least one othernode. FIG. 13 depicts several sample components that may be employed tofacilitate communication between nodes. Specifically, FIG. 13illustrates a wireless device 1310 (e.g., an access point) and awireless device 1350 (e.g., an access terminal) of a MIMO system 1300.At the device 1310, traffic data for a number of data streams isprovided from a data source 1312 to a transmit (“TX”) data processor1314.

In some aspects, each data stream is transmitted over a respectivetransmit antenna. The TX data processor 1314 formats, codes, andinterleaves the traffic data for each data stream based on a particularcoding scheme selected for that data stream to provide coded data.

The coded data for each data stream may be multiplexed with pilot datausing OFDM techniques. The pilot data is typically a known data patternthat is processed in a known manner and may be used at the receiversystem to estimate the channel response. The multiplexed pilot and codeddata for each data stream is then modulated (i.e., symbol mapped) basedon a particular modulation scheme (e.g., BPSK, QSPK, M-PSK, or M-QAM)selected for that data stream to provide modulation symbols. The datarate, coding, and modulation for each data stream may be determined byinstructions performed by a processor 1330. A data memory 1332 may storeprogram code, data, and other information used by the processor 1330 orother components of the device 1310.

The modulation symbols for all data streams are then provided to a TXMIMO processor 1320, which may further process the modulation symbols(e.g., for OFDM). The TX MIMO processor 1320 then provides N_(T)modulation symbol streams to N_(T) transceivers (“XCVR”) 1322A through1322T. In some aspects, the TX MIMO processor 1320 applies beam-formingweights to the symbols of the data streams and to the antenna from whichthe symbol is being transmitted.

Each transceiver 1322 receives and processes a respective symbol streamto provide one or more analog signals, and further conditions (e.g.,amplifies, filters, and upconverts) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. N_(T)modulated signals from transceivers 1322A through 1322T are thentransmitted from N_(T) antennas 1324A through 1324T, respectively.

At the device 1350, the transmitted modulated signals are received byN_(R) antennas 1352A through 1352R and the received signal from eachantenna 1352 is provided to a respective transceiver (“XCVR”) 1354Athrough 1354R. Each transceiver 1354 conditions (e.g., filters,amplifies, and downconverts) a respective received signal, digitizes theconditioned signal to provide samples, and further processes the samplesto provide a corresponding “received” symbol stream.

A receive (“RX”) data processor 1360 then receives and processes theN_(R) received symbol streams from N_(R) transceivers 1354 based on aparticular receiver processing technique to provide N_(T) “detected”symbol streams. The RX data processor 1360 then demodulates,deinterleaves, and decodes each detected symbol stream to recover thetraffic data for the data stream. The processing by the RX dataprocessor 1360 is complementary to that performed by the TX MIMOprocessor 1320 and the TX data processor 1314 at the device 1310.

A processor 1370 periodically determines which pre-coding matrix to use(discussed below). The processor 1370 formulates a reverse link messagecomprising a matrix index portion and a rank value portion. A datamemory 1372 may store program code, data, and other information used bythe processor 1370 or other components of the device 1350.

The reverse link message may comprise various types of informationregarding the communication link and/or the received data stream. Thereverse link message is then processed by a TX data processor 1338,which also receives traffic data for a number of data streams from adata source 1336, modulated by a modulator 1380, conditioned by thetransceivers 1354A through 1354R, and transmitted back to the device1310.

At the device 1310, the modulated signals from the device 1350 arereceived by the antennas 1324, conditioned by the transceivers 1322,demodulated by a demodulator (“DEMOD”) 1340, and processed by a RX dataprocessor 1342 to extract the reverse link message transmitted by thedevice 1350. The processor 1330 then determines which pre-coding matrixto use for determining the beam-forming weights then processes theextracted message.

FIG. 13 also illustrates that the communication components may includeone or more components that perform power control operations as taughtherein. For example, a power control component 1390 may cooperate withthe processor 1330 and/or other components of the device 1310 tosend/receive signals to/from another device (e.g., device 1350) astaught herein. Similarly, a power control component 1392 may cooperatewith the processor 1370 and/or other components of the device 1350 tosend/receive signals to/from another device (e.g., device 1310). Itshould be appreciated that for each device 1310 and 1350 thefunctionality of two or more of the described components may be providedby a single component. For example, a single processing component mayprovide the functionality of the power control component 1390 and theprocessor 1330 and a single processing component may provide thefunctionality of the power control component 1392 and the processor1370.

The teachings herein may be incorporated into various types ofcommunication systems and/or system components. In some aspects, theteachings herein may be employed in a multiple-access system capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., by specifying one or more of bandwidth, transmitpower, coding, interleaving, and so on). For example, the teachingsherein may be applied to any one or combinations of the followingtechnologies: Code Division Multiple Access (“CDMA”) systems,Multiple-Carrier CDMA (“MCCDMA”), Wideband CDMA (“W-CDMA”), High-SpeedPacket Access (“HSPA,” “HSPA+”) systems, High-Speed Downlink PacketAccess (“HSDPA”) systems, Time Division Multiple Access (“TDMA”)systems, Frequency Division Multiple Access (“FDMA”) systems,Single-Carrier FDMA (“SC-FDMA”) systems, Orthogonal Frequency DivisionMultiple Access (“OFDMA”) systems, or other multiple access techniques.A wireless communication system employing the teachings herein may bedesigned to implement one or more standards, such as IS-95, cdma2000,IS-856, W-CDMA, TDSCDMA, and other standards. A CDMA network mayimplement a radio technology such as Universal Terrestrial Radio Access(“UTRA)”, cdma2000, or some other technology. UTRA includes W-CDMA andLow Chip Rate (“LCR”). The cdma2000 technology covers IS-2000, IS-95 andIS-856 standards. A TDMA network may implement a radio technology suchas Global System for Mobile Communications (“GSM”). An OFDMA network mayimplement a radio technology such as Evolved UTRA (“E-UTRA”), IEEE802.11, IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, andGSM are part of Universal Mobile Telecommunication System (“UMTS”). Theteachings herein may be implemented in a 3GPP Long Term Evolution(“LTE”) system, an Ultra-Mobile Broadband (“UMB”) system, and othertypes of systems. LTE is a release of UMTS that uses E-UTRA. Althoughcertain aspects of the disclosure may be described using 3GPPterminology, it is to be understood that the teachings herein may beapplied to 3GPP (Re199, Re15, Re16, Re17) technology, as well as 3GPP2(IxRTT, 1xEV-DO RelO, RevA, RevB) technology and other technologies.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of apparatuses (e.g., nodes). For example, anaccess node as discussed herein may be configured or referred to as anaccess point (“AP”), base station (“BS”), NodeB, radio networkcontroller (“RNC”), eNodeB, base station controller (“BSC”), basetransceiver station (“BTS”), transceiver function (“TF”), radio router,radio transceiver, basic service set (“BSS”), extended service set(“ESS”), radio base station (“RBS”), a femto node, a pico node, or someother terminology.

In addition, an access terminal as discussed herein may be referred toas a mobile station, user equipment, subscriber unit, subscriberstation, remote station, remote terminal, user terminal, user agent, oruser device. In some implementations such a node may consist of, beimplemented within, or include a cellular telephone, a cordlesstelephone, a Session Initiation Protocol (“SIP”) phone, a wireless localloop (“WLL”) station, a personal digital assistant (“PDA”), a handhelddevice having wireless connection capability, or some other suitableprocessing device connected to a wireless modem.

Accordingly, one or more aspects taught herein may consist of, beimplemented within, or include variety types of apparatuses. Such anapparatus may comprise a phone (e.g., a cellular phone or smart phone),a computer (e.g., a laptop), a portable communication device, a portablecomputing device (e.g., a personal data assistant), an entertainmentdevice (e.g., a music or video device, or a satellite radio), a globalpositioning system device, or any other suitable device that isconfigured to communicate via a wireless medium.

As mentioned above, in some aspects a wireless node may comprise anaccess node (e.g., an access point) for a communication system. Such anaccess node may provide, for example, connectivity for or to a network(e.g., a wide area network such as the Internet or a cellular network)via a wired or wireless communication link. Accordingly, the access nodemay enable another node (e.g., an access terminal) to access the networkor some other functionality. In addition, it should be appreciated thatone or both of the nodes may be portable or, in some cases, relativelynon-portable. Also, it should be appreciated that a wireless node (e.g.,a wireless device) also may be capable of transmitting and/or receivinginformation in a non-wireless manner via an appropriate communicationinterface (e.g., via a wired connection).

A wireless node may communicate via one or more wireless communicationlinks that are based on or otherwise support any suitable wirelesscommunication technology. For example, in some aspects a wireless nodemay associate with a network. In some aspects the network may comprise alocal area network or a wide area network. A wireless device may supportor otherwise use one or more of a variety of wireless communicationtechnologies, protocols, or standards such as those discussed herein(e.g., CDMA, TDMA, OFDM, OFDMA, WiMAX, Wi-Fi, and so on). Similarly, awireless node may support or otherwise use one or more of a variety ofcorresponding modulation or multiplexing schemes. A wireless node maythus include appropriate components (e.g., air interfaces) to establishand communicate via one or more wireless communication links using theabove or other wireless communication technologies. For example, awireless node may comprise a wireless transceiver with associatedtransmitter and receiver components that may include various components(e.g., signal generators and signal processors) that facilitatecommunication over a wireless medium.

The components described herein may be implemented in a variety of ways.Referring to FIGS. 14-15, apparatuses 1400-1500 are represented as aseries of interrelated functional blocks. In some aspects thefunctionality of these blocks may be implemented as a processing systemincluding one or more processor components. In some aspects thefunctionality of these blocks may be implemented using, for example, atleast a portion of one or more integrated circuits (e.g., an ASIC). Asdiscussed herein, an integrated circuit may include a processor,software, other related components, or some combination thereof. Thefunctionality of these blocks also may be implemented in some othermanner as taught herein.

The apparatuses 1400-1500 may include one or more modules that mayperform one or more of the functions described above with regard tovarious figures. For example, a maximum received signal strengthdetermining means 1402 may correspond to, for example, a received signalstrength determiner as discussed herein. A total received signalstrength determining means 1404 may correspond to, for example, a totalsignal strength determiner as discussed herein. A transmit powerdetermining means 1406 may correspond to, for example, a transmit powercontroller as discussed herein. A receiving means 1502 may correspondto, for example, a receiver as discussed herein. An identifying means1504 may correspond to, for example, a transmit power controller asdiscussed herein. A transmitting means 1506 may correspond to, forexample, a transmitter as discussed herein.

It should be understood that any reference to an element herein using adesignation such as “first,” “second,” and so forth does not generallylimit the quantity or order of those elements. Rather, thesedesignations may be used herein as a convenient method of distinguishingbetween two or more elements or instances of an element. Thus, areference to first and second elements does not mean that only twoelements may be employed there or that the first element must precedethe second element in some manner. Also, unless stated otherwise a setof elements may comprise one or more elements.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that any of the variousillustrative logical blocks, modules, processors, means, circuits, andalgorithm steps described in connection with the aspects disclosedherein may be implemented as electronic hardware (e.g., a digitalimplementation, an analog implementation, or a combination of the two,which may be designed using source coding or some other technique),various forms of program or design code incorporating instructions(which may be referred to herein, for convenience, as “software” or a“software module”), or combinations of both. To clearly illustrate thisinterchangeability of hardware and software, various illustrativecomponents, blocks, modules, circuits, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the aspects disclosed herein may be implementedwithin or performed by an integrated circuit (“IC”), an access terminal,or an access point. The IC may comprise a general purpose processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, electrical components, optical components,mechanical components, or any combination thereof designed to performthe functions described herein, and may execute codes or instructionsthat reside within the IC, outside of the IC, or both. A general purposeprocessor may be a microprocessor, but in the alternative, the processormay be any conventional processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of a DSP and a microprocessor, aplurality of microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration.

It is understood that any specific order or hierarchy of steps in anydisclosed process is an example of a sample approach. Based upon designpreferences, it is understood that the specific order or hierarchy ofsteps in the processes may be rearranged while remaining within thescope of the present disclosure. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

The functions described may be implemented in hardware, software,firmware, or any combination thereof. If implemented in software, thefunctions may be stored on or transmitted over as one or moreinstructions or code on a computer-readable medium. Computer-readablemedia includes both computer storage media and communication mediaincluding any medium that facilitates transfer of a computer programfrom one place to another. A storage media may be any available mediathat can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media. In summary, it should be appreciated that acomputer-readable medium may be implemented in any suitablecomputer-program product.

The previous description of the disclosed aspects is provided to enableany person skilled in the art to make or use the present disclosure.Various modifications to these aspects will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other aspects without departing from the scope of thedisclosure. Thus, the present disclosure is not intended to be limitedto the aspects shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

1. (canceled)
 2. A method of wireless communication, comprising:receiving at a home femto node a measurement report from a home accessterminal, the measurement report conveying transmit power measurementsof neighboring femto nodes taken by the home access terminal; rankingthe neighboring femto nodes based on the measurement report according totheir respective transmit powers; and sending a message to the highestranking neighboring femto node requesting a reduction in transmit power.3. The method of claim 2, wherein the highest ranking neighboring femtonode is associated with the highest transmit power measurement in themeasurement report.
 4. The method of claim 2, further comprisingtransmitting a measurement report request to the home access terminal torequest the measurement report.
 5. The method of claim 2, furthercomprising: monitoring received signal conditions at the home accessterminal; and initiating the ranking and the sending in response to thereceived signal conditions being below an acceptable threshold.
 6. Themethod of claim 2, further comprising monitoring for an acknowledgementmessage from the highest ranking neighboring femto node confirming thereduction in transmit power.
 7. The method of claim 6, furthercomprising: re-ranking the neighboring femto nodes to exclude thehighest ranking femto node in response to a negative acknowledgementmessage being received or no acknowledgement message being received; andsending a message to the new highest ranking neighboring femto noderequesting a reduction in transmit power.
 8. The method of claim 2,further comprising: receiving at the home femto node a message from oneof the neighboring femto nodes requesting a reduction in transmit power;and estimating received signal conditions at the home access terminal inaccordance with the requested reduction in transmit power.
 9. The methodof claim 8, further comprising: sending an acknowledgment message to theone of the neighboring femto nodes in response to the estimated receivedsignal conditions being above an acceptable threshold; and reducing atransmit power of the home femto node in accordance with the requestedreduction in transmit power.
 10. The method of claim 8, furthercomprising sending a negative acknowledgment message to the one of theneighboring femto nodes in response to the estimated received signalconditions being below an acceptable threshold.
 11. The method of claim10, further comprising reducing a transmit power of the home femto nodeby an amount less than the requested reduction in transmit power,wherein the negative acknowledgment message includes an indication ofthe amount by which the transmit power is reduced.
 12. An apparatus ofwireless communication, comprising: a processor configured to: receiveat a home femto node a measurement report from a home access terminal,the measurement report conveying transmit power measurements ofneighboring femto nodes taken by the home access terminal, rank theneighboring femto nodes based on the measurement report according totheir respective transmit powers, and send a message to the highestranking neighboring femto node requesting a reduction in transmit power;and memory coupled to the processor and configured to store related dataand instructions.
 13. The apparatus of claim 12, wherein the highestranking neighboring femto node is associated with the highest transmitpower measurement in the measurement report.
 14. The apparatus of claim12, wherein the processor is further configured to transmit ameasurement report request to the home access terminal to request themeasurement report.
 15. The apparatus of claim 12, wherein the processoris further configured to: monitor received signal conditions at the homeaccess terminal; and initiate the ranking and the sending in response tothe received signal conditions being below an acceptable threshold. 16.The apparatus of claim 12, wherein the processor is further configuredto monitor for an acknowledgement message from the highest rankingneighboring femto node confirming the reduction in transmit power. 17.The apparatus of claim 16, wherein the processor is further configuredto: re-rank the neighboring femto nodes to exclude the highest rankingfemto node in response to a negative acknowledgement message beingreceived or no acknowledgement message being received; and send amessage to the new highest ranking neighboring femto node requesting areduction in transmit power.
 18. The apparatus of claim 12, wherein theprocessor is further configured to: receive at the home femto node amessage from one of the neighboring femto nodes requesting a reductionin transmit power; and estimate received signal conditions at the homeaccess terminal in accordance with the requested reduction in transmitpower.
 19. The apparatus of claim 18, wherein the processor is furtherconfigured to: send an acknowledgment message to the one of theneighboring femto nodes in response to the estimated received signalconditions being above an acceptable threshold; and reduce a transmitpower of the home femto node in accordance with the requested reductionin transmit power.
 20. The apparatus of claim 18, wherein the processoris further configured to send a negative acknowledgment message to theone of the neighboring femto nodes in response to the estimated receivedsignal conditions being below an acceptable threshold.
 21. The apparatusof claim 20, wherein the processor is further configured to reduce atransmit power of the home femto node by an amount less than therequested reduction in transmit power, wherein the negativeacknowledgment message includes an indication of the amount by which thetransmit power is reduced.
 22. An apparatus of wireless communication,comprising: means for receiving at a home femto node a measurementreport from a home access terminal, the measurement report conveyingtransmit power measurements of neighboring femto nodes taken by the homeaccess terminal; means for ranking the neighboring femto nodes based onthe measurement report according to their respective transmit powers;and means for sending a message to the highest ranking neighboring femtonode requesting a reduction in transmit power.
 23. The apparatus ofclaim 22, wherein the highest ranking neighboring femto node isassociated with the highest transmit power measurement in themeasurement report.
 24. The apparatus of claim 22, further comprisingmeans for transmitting a measurement report request to the home accessterminal to request the measurement report.
 25. The apparatus of claim22, further comprising: means for monitoring received signal conditionsat the home access terminal; and means for initiating the ranking andthe sending in response to the received signal conditions being below anacceptable threshold.
 26. The apparatus of claim 22, further comprisingmeans for monitoring for an acknowledgement message from the highestranking neighboring femto node confirming the reduction in transmitpower.
 27. The apparatus of claim 26, further comprising: means forre-ranking the neighboring femto nodes to exclude the highest rankingfemto node in response to a negative acknowledgement message beingreceived or no acknowledgement message being received; and means forsending a message to the new highest ranking neighboring femto noderequesting a reduction in transmit power.
 28. The apparatus of claim 22,further comprising: means for receiving at the home femto node a messagefrom one of the neighboring femto nodes requesting a reduction intransmit power; and means for estimating received signal conditions atthe home access terminal in accordance with the requested reduction intransmit power.
 29. The apparatus of claim 28, further comprising: meansfor sending an acknowledgment message to the one of the neighboringfemto nodes in response to the estimated received signal conditionsbeing above an acceptable threshold; and means for reducing a transmitpower of the home femto node in accordance with the requested reductionin transmit power.
 30. The apparatus of claim 28, further comprisingmeans for sending a negative acknowledgment message to the one of theneighboring femto nodes in response to the estimated received signalconditions being below an acceptable threshold.
 31. The apparatus ofclaim 30, further comprising means for reducing a transmit power of thehome femto node by an amount less than the requested reduction intransmit power, wherein the negative acknowledgment message includes anindication of the amount by which the transmit power is reduced.
 32. Annon-transitory computer-readable medium comprising code, which, whenexecuted by a processor, causes the processor to perform operations forwireless communication, the non-transitory computer-readable mediumcomprising: code for receiving at a home femto node a measurement reportfrom a home access terminal, the measurement report conveying transmitpower measurements of neighboring femto nodes taken by the home accessterminal; code for ranking the neighboring femto nodes based on themeasurement report according to their respective transmit powers; andcode for sending a message to the highest ranking neighboring femto noderequesting a reduction in transmit power.
 33. The non-transitorycomputer-readable medium of claim 32, wherein the highest rankingneighboring femto node is associated with the highest transmit powermeasurement in the measurement report.
 34. The non-transitorycomputer-readable medium of claim 32, further comprising code fortransmitting a measurement report request to the home access terminal torequest the measurement report.
 35. The non-transitory computer-readablemedium of claim 32, further comprising: code for monitoring receivedsignal conditions at the home access terminal; and code for initiatingthe ranking and the sending in response to the received signalconditions being below an acceptable threshold.
 36. The non-transitorycomputer-readable medium of claim 32, further comprising code formonitoring for an acknowledgement message from the highest rankingneighboring femto node confirming the reduction in transmit power. 37.The non-transitory computer-readable medium of claim 36, furthercomprising: code for re-ranking the neighboring femto nodes to excludethe highest ranking femto node in response to a negative acknowledgementmessage being received or no acknowledgement message being received; andcode for sending a message to the new highest ranking neighboring femtonode requesting a reduction in transmit power.
 38. The non-transitorycomputer-readable medium of claim 32, further comprising: code forreceiving at the home femto node a message from one of the neighboringfemto nodes requesting a reduction in transmit power; and code forestimating received signal conditions at the home access terminal inaccordance with the requested reduction in transmit power.
 39. Thenon-transitory computer-readable medium of claim 38, further comprising:code for sending an acknowledgment message to the one of the neighboringfemto nodes in response to the estimated received signal conditionsbeing above an acceptable threshold; and code for reducing a transmitpower of the home femto node in accordance with the requested reductionin transmit power.
 40. The non-transitory computer-readable medium ofclaim 38, further comprising code for sending a negative acknowledgmentmessage to the one of the neighboring femto nodes in response to theestimated received signal conditions being below an acceptablethreshold.
 41. The non-transitory computer-readable medium of claim 30,further comprising code for reducing a transmit power of the home femtonode by an amount less than the requested reduction in transmit power,wherein the negative acknowledgment message includes an indication ofthe amount by which the transmit power is reduced.